基于zookeeper的分布式锁实现

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工作中需要写一个定时任务,由于是集群环境,自然而然想到需要通过分布式锁来保证单台执行..相信大家都会想到使用zk来实现对应的分布式锁.下面就简单介绍一下几种实现

准备工作

有几个帮助类,先把代码放上来

ZKClient 对zk的操作做了一个简单的封装

package zk.lock;

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import zk.util.ZKUtil;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

/**
 * User: zhenghui
 * Date: 14-3-26
 * Time: 下午8:50
 * 封装一个zookeeper实例.
 */
public class ZKClient implements Watcher {

    private ZooKeeper zookeeper;

    private CountDownLatch connectedSemaphore = new CountDownLatch(1);


    public ZKClient(String connectString, int sessionTimeout) throws Exception {
        zookeeper = new ZooKeeper(connectString, sessionTimeout, this);
        System.out.println("connecting zk server");
        if (connectedSemaphore.await(10l, TimeUnit.SECONDS)) {
            System.out.println("connect zk server success");
        } else {
            System.out.println("connect zk server error.");
            throw new Exception("connect zk server error.");
        }
    }

    public void close() throws InterruptedException {
        if (zookeeper != null) {
            zookeeper.close();
        }
    }

    public void createPathIfAbsent(String path, boolean isPersistent) throws Exception {
        CreateMode createMode = isPersistent ? CreateMode.PERSISTENT : CreateMode.EPHEMERAL;
        path = ZKUtil.normalize(path);
        if (!this.exists(path)) {
            zookeeper.create(path, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, createMode);
        }
    }

    public boolean exists(String path) throws Exception {
        path = ZKUtil.normalize(path);
        Stat stat = zookeeper.exists(path, null);
        return stat != null;
    }

    public String getData(String path) throws Exception {
        path = ZKUtil.normalize(path);
        try {
            byte[] data = zookeeper.getData(path, null, null);
            return new String(data);
        } catch (KeeperException e) {
            if (e instanceof KeeperException.NoNodeException) {
                throw new Exception("Node does not exist,path is [" + e.getPath() + "].", e);
            } else {
                throw new Exception(e);
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new Exception(e);
        }
    }

    @Override
    public void process(WatchedEvent event) {
        if (event == null) return;

        // 连接状态
        Watcher.Event.KeeperState keeperState = event.getState();
        // 事件类型
        Watcher.Event.EventType eventType = event.getType();
        // 受影响的path
//        String path = event.getPath();
        if (Watcher.Event.KeeperState.SyncConnected == keeperState) {
            // 成功连接上ZK服务器
            if (Watcher.Event.EventType.None == eventType) {
                System.out.println("zookeeper connect success");
                connectedSemaphore.countDown();
            }
        }
        //下面可以做一些重连的工作.
        else if (Watcher.Event.KeeperState.Disconnected == keeperState) {
            System.out.println("zookeeper Disconnected");
        } else if (Watcher.Event.KeeperState.AuthFailed == keeperState) {
            System.out.println("zookeeper AuthFailed");
        } else if (Watcher.Event.KeeperState.Expired == keeperState) {
            System.out.println("zookeeper Expired");
        }
    }
}

ZKUtil 针对zk路径的一个工具类

package zk.util;

/**
 * User: zhenghui
 * Date: 14-3-26
 * Time: 下午9:56
 */
public class ZKUtil {

    public static final String SEPARATOR = "/";

    /**
     * 转换path为zk的标准路径 以/开头,最后不带/
     */
    public static String normalize(String path) {
        String temp = path;
        if(!path.startsWith(SEPARATOR)) {
            temp = SEPARATOR + path;
        }
        if(path.endsWith(SEPARATOR)) {
            temp = temp.substring(0, temp.length()-1);
            return normalize(temp);
        }else {
            return temp;
        }
    }

    /**
     * 链接两个path,并转化为zk的标准路径
     */
    public static String contact(String path1,String path2){
        if(path2.startsWith(SEPARATOR)) {
            path2 = path2.substring(1);
        }
        if(path1.endsWith(SEPARATOR)) {
            return normalize(path1 + path2);
        } else {
            return normalize(path1 + SEPARATOR + path2);
        }
    }

    /**
     * 字符串转化成byte类型
     */
    public static byte[] toBytes(String data) {
        if(data == null || data.trim().equals("")) return null;
        return data.getBytes();
    }
}

NetworkUtil 获取本机IP的工具方法

package zk.util;

import java.net.InetAddress;
import java.net.NetworkInterface;
import java.util.Enumeration;

/**
 * User: zhenghui
 * Date: 14-4-1
 * Time: 下午4:47
 */
public class NetworkUtil {

    static private final char COLON = ':';

    /**
     * 获取当前机器ip地址
     * 据说多网卡的时候会有问题.
     */
    public static String getNetworkAddress() {
        Enumeration<NetworkInterface> netInterfaces;
        try {
            netInterfaces = NetworkInterface.getNetworkInterfaces();
            InetAddress ip;
            while (netInterfaces.hasMoreElements()) {
                NetworkInterface ni = netInterfaces
                        .nextElement();
                Enumeration<InetAddress> addresses=ni.getInetAddresses();
                while(addresses.hasMoreElements()){
                    ip = addresses.nextElement();
                    if (!ip.isLoopbackAddress()
                            && ip.getHostAddress().indexOf(COLON) == -1) {
                        return ip.getHostAddress();
                    }
                }
            }
            return "";
        } catch (Exception e) {
            return "";
        }
    }
}

--------------------------- 正文开始 -----------------------------------

这种实现非常简单,具体的流程如下

对应的实现如下

package zk.lock;


import zk.util.NetworkUtil;
import zk.util.ZKUtil;

/**
 * User: zhenghui
 * Date: 14-3-26
 * Time: 下午8:37
 * 分布式锁实现.
 *
 * 这种实现的原理是,创建某一个任务的节点,比如 /lock/tasckname 然后获取对应的值,如果是当前的Ip,那么获得锁,如果不是,则没获得
 * .如果该节点不存在,则创建该节点,并把改节点的值设置成当前的IP
 */
public class DistributedLock01 {

    private ZKClient zkClient;


    public static final String LOCK_ROOT = "/lock";
    private String lockName;


    public DistributedLock01(String connectString, int sessionTimeout,String lockName) throws Exception {
        //先创建zk链接.
        this.createConnection(connectString,sessionTimeout);

        this.lockName = lockName;
    }

    public boolean tryLock(){
        String path = ZKUtil.contact(LOCK_ROOT,lockName);
        String localIp = NetworkUtil.getNetworkAddress();
        try {
            if(zkClient.exists(path)){
                String ownnerIp = zkClient.getData(path);
                if(localIp.equals(ownnerIp)){
                    return true;
                }
            } else {
                zkClient.createPathIfAbsent(path,false);
                if(zkClient.exists(path)){
                    String ownnerIp = zkClient.getData(path);
                    if(localIp.equals(ownnerIp)){
                        return true;
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }


    /**
     * 创建zk连接
     *
     */
    protected void createConnection(String connectString, int sessionTimeout) throws Exception {
        if(zkClient != null){
            releaseConnection();
        }
        zkClient = new ZKClient(connectString,sessionTimeout);
        zkClient.createPathIfAbsent(LOCK_ROOT,true);
    }
    /**
     * 关闭ZK连接
     */
    protected void releaseConnection() throws InterruptedException {
        if (zkClient != null) {
            zkClient.close();
        }
    }

}

总结

网上有很多文章,大家的方法大多数都是创建一个root根节点,每一个trylock的客户端都会在root下创建一个 EPHEMERAL_SEQUENTIAL 的子节点,同时设置root的child 变更watcher(为了避免羊群效应,可以只添加前一个节点的变更通知) .如果创建的节点的序号是最小,则获取到锁,否则继续等待root的child 变更..这种方式我个人觉得有点繁琐,实现起来有点麻烦.具体的现有实现可以查看

https://svn.apache.org/repos/asf/zookeeper/trunk/src/recipes/lock/

其他的,想了半天没啥好说的..over